1. Field of the Invention
The invention relates to a polymerizable liquid crystal composition and uses for the same, more specifically to a polymerizable liquid crystal composition which reflects light of a specific wavelength in the vicinity of room temperature, a polymer including the above composition and uses for the above polymer.
2. Related Art
A cholesteric liquid crystal molecule has a spiral structure in a liquid crystal state. Accordingly, when a cholesteric liquid crystal phase is irradiated with light, it reflects a circular polarizing light of a specific wavelength corresponding to a spiral rotational direction of the liquid crystal molecule and a length of the pitch. For example, when irradiated with a visible light, it reflects selectively lights having wavelengths of blue, green, yellow and red corresponding to a length of a pitch in the liquid crystal. The color tones thereof are different from those of pigments and dyes which take on colors by absorption of lights and have a visual dependency in which a color tone changes according to viewing angles. Further, a length of a pitch in cholesteric liquid crystal can be controlled by temperature and the kind of compounds, and therefore it can selectively reflect not only visible lights but also lights of near infrared and ultraviolet regions.
There have been materials which selectively reflect lights of various wavelengths in a broad wavelength region making use of the characteristics of the cholesteric liquid crystal. They are, for example, liquid crystal pigments, coating materials, spray inks, print inks, cosmetics, printed matters for preventing counterfeit, ornamental articles and the like. Further, they are proposed as well for polarizing plates in optical devices such as liquid crystal displays and holographic devices, compensation plates, optical films such as color filters and the like. In the case of a cholesteric liquid crystal pigment which is an existing material, flake-shaped cholesteric liquid crystal polymers and microencapsulated cholesteric liquid crystal are used. The uses thereof include coating materials for cars, cosmetic ingredients and the like.
A polymer of a mixture including a chiral polymerizable mesogen compound having an optically active group, a non-chiral polymerizable mesogen compound, a photoinitiator and the like is described as a pigment which is processed in a flake form in JP 2000-505485 T (Patent Document 1; WO 97/30136). In Patent Document 1, the kind of chiral polymerizable mesogen compound and the content thereof in the mixture are changed to thereby control the pitch in a spiral of cholesteric liquid crystal and obtain a pigment having a desired color tone.
Further, a microencapsulated liquid crystal material is described in JP H8-24625 A/1996 (Patent Document 2). The above material has a structure in which a copolymer of glutamic γ-ester having a thermotropic cholesteric liquid crystallinity is covered with a film including an epoxy resin and amine as structural components. The glutamic γ-ester copolymer has a high cohesive property and therefore has to be aligned by applying a shearing stress after being molten in order to solidify it. In Patent Document 2, however, cohesion can be avoided by microencapsulation, and the operability in solidification is enhanced.
The above flake-shaped or microencapsulated liquid crystal material is used as a color material for coating materials, ink components and cosmetic ingredients. However, a flake-shaped pigment used as a color material is produced by forming a cholesteric polymer layer on a support, peeling it and then crushing the polymer layer. A microcapsule is produced by forming a resin coating film on a cholesteric liquid crystal material. Further, a process of a multistage in which they are dispersed once in a solvent, coated on an object material and fixed is required.
In contrast with this, in JP H10-508882 T/1998 (Patent Document 3; U.S. Pat. No. 5,798,147), a composition including a polymerizable liquid crystal monomer and a chiral liquid crystal monomer or a chiral non-liquid crystal monomer is applied directly or after being dissolved in a solvent on a support at a relatively low temperature, and it is then cured by an energy beam. In Patent Document 3, a composition including a mixture of tricyclic liquid crystalline compounds in which a nematic phase area is 90° C. or higher and a chiral monomer is used in examples. Further, in mixing the respective components of the composition, they are dissolved in dichloromethane and then subjected once to heat treatment up to 70° C. A cholesteric material which is a color material preferably exhibits a stable cholesteric liquid crystal phase in the vicinity of room temperature in order to carry out coating and print treatment in the vicinity of room temperature of a relatively low temperature.
A composition including 2 to 3 components of polymerizable liquid crystal monomers which are cholesterol derivatives is described as the above material in JP S59-109505 A/1984 (Patent Document 4; U.S. Pat. No. 4,637,896). Among them, a 1: 1 mixture of a compound Va and a compound Ve each described in Example 7 exhibits a cholesteric phase in a wide temperature range and realizes fixation of cholesteric colors of blue, green and orange by photocuring in a range of 10 to 32° C. in the vicinity of room temperature. In the method of the Patent Document 4, however, the temperature of the materials has to be controlled at an interval of 5° C. in curing in order to obtain the targeted polymer, and a polymer which takes on specific reflected colors of red, green and blue at a fixed room temperature has not been obtained.